Schunk Carbon Technology SiC30 – Silicon Carbide / Graphite Composite Material schunk-carbontechnology.com SIC30 – SILICON CARBIDE/GRAPHITE COMPOSITE MATERIAL Schunk Carbon Technology: SiC30 – An Extraordinary Silicon Always at your side. Carbide/Graphite Composite Material Schunk Carbon Technology focuses on development, manufacture and application of carbon and ceramic solutions. It combines innovative Applications spirit and technological expertise with exceptional customer service to The main fields of application of the SiC30 material are provide a range of products and services unique to the market. sliding rings and bearings for use in media with a poor lubri- cating capacity. The combination of excellent properties of graphite (good emergency-running properties, thermal In Schunk Carbon Technology, you have a partner who can offer all the technological possibilities of an international company and implement ideas custom-tailored to your shock resistance, etc.) and silicon carbide (hardness, needs, both for high-volume industrial markets and for highly specialized niche markets. strength, abrasion resistance) combined with an exceptional structure allows solving problems that would not be possib- le with other materials. The best results are often achieved with the material pairing of SiC30 to SiC30. Production The material SiC30 is produced by impregnating a highly Figure 1: Structural pattern of graphite and silicon carbide A Schunk Group division porous electro-graphite with molten silicon. At the same time that the silicon penetrates into the pores, there is a Physical Properties Enabling, idea-driven, cooperative – chemical reaction that changes the silicon and carbon into If you hope to apply technology to silicon carbide. The process continues until the pores are Bulk density [g/cm3] 2.65 develop better products and capture closed by the silicon carbide that has been formed. new markets, we can help. Porosity [Vol.-%] — Flexural strength [N/mm2] 140 Composition The main components of the material are silicon carbide Compressive strength [N/mm2] 500 The Schunk Group has been supporting customers with innovative technologies since with about 62% and about 35% graphite; the proportion of Young’s modulus (dyn.) [kN/mm2] 140 1913. As an idea-driven technology company, free silicon is about 3% (in each case, part by weight). This consists of a hard SiC- and a soft Hardness innovation is fundamental to our culture. We represents a volume share of about 53% silicon carbide, graphite phase forge long-lasting, cooperative working about 43% graphite and about 4% silicon. The silicon Temperature resistance relationships with our clients. carbide is present to about 95% in the cubic β-SiC oxidizing atmosphere °C 500 inert atmosphere °C 2300 modification. SiC30 is completely free of boron and is You will find our custom-tailored, high-tech Coefficient of thermal products and systems in markets such as; carbon thus also suitable for applications in the manufacture expansion technology and ceramics, environment of silicon for the electronics industry. α 20 – 200 °C [10–6/K] 3.0 –6 simulation and air-conditioning technology, α 20 – 1000 °C [10 /K] 4.0 sintered metal and ultrasonic welding. The Structure Thermal conductivity [W/mK] 125 Schunk Group is active in a large number of key The unique thing about the structure is an interpenetrating Spec. electr. resistance [μΩm] 120 industries, from automotive, rail, aviation and network of graphite and silicon carbide (relics of coherent marine technologies to solar and wind energy to These data are provided as typical values based on our experience. As with any raw carbon structure or the pore system of the electro-graphite). material or manufacturing process, variations can occur. Consequently, such values are the chemical and machine production industries. not guaranteed and are subject to change without notice. Our 8,000 employees in 29 countries are ready Free silicon is merely present in the form of small islands to serve you. that are enclosed in the silicon carbide phase. Table 1: Physical Properties of SiC30 (Typical Data) 02 03 SIC30 – SILICON CARBIDE/GRAPHITE COMPOSITE MATERIAL Running behavior under marginal lubricated conditions Emergency running properties of hard sliding For materials that have absolutely no or a poor amount materials such as silicon carbide ceramics can of emergency running capabilities, the friction increases be excellently characterized with a high- sharply at an early stage and marks the end of the test. pressure face seal test (see Figure 2). The diagram in Figure 3 illustrates this with the examp- le of a commercially available sintered silicon carbide (SSiC). SiC30, however, does not show this effect in any way. Lubrication is also maintained under critical conditions, Sliding speed: 9.35 m/s an effect of the high graphite content in conjunction Balance ratio: 0.79 with a unique material structure (see Figure 5). Media: demineralized water Media temperature: 20 – 95° C Figure 4: SSiC structure Figure 5: Structural pattern Media pressure: 5 – 100 bar of graphite and silicon carbide During the testing process, the pressure on and temperature of the media were successively increased, thereby generating inadequate lubrication conditions. Figure 2: High-pressure face seal test rig The gage for determining the emercency running proper- ties is the duration that it took to achieve a seal pairing of the tested material under these severe conditions without abrupt power peaks. SiC30 — a C-SiC composite material with excellent emergency running properties — 1010 120 99 100 88 77 80 66 LeistungPower SiC30SiC30 55 60 C bzw. Druck in bar Druckin bzw. C ° Leistung Power SSiC Leistung in kW Druck Pressure (bar) in bar Power in kW Power 44 TemperaturTemperature (°C) in °C 40 33 in Temperatur Temperature in °C and pressure in bar in °C and pressure Temperature Figure 6: Sealing rings of SiC30 22 20 11 0 0 0 0,00,0 0,50,5 1,0 1,5 2,0 2,52,5 VersuchszeitTime in h in h Figure 3: Diagram of the test run with SiC30 and SSiC 04 05 SIC30 – SILICON CARBIDE/GRAPHITE COMPOSITE MATERIAL Blister Resistant Thermal Shock Behaviour The thermal shock resistance as a characteristic material property is proportional to the mate- Blistering is one of the most common causes of failure for carbon sealing rings in sliding gaskets. rial’s strength and thermal conductivity but in inverse proportion to its Young‘s modulus and coefficient of thermal expansion. However, in tribological applications, materials with dry or The Testing Procedure emergency-running properties – and thus on carbon materi- The resistance of tribological materials to thermal shock can be determined, among other things, by means of a comparative als – are often indispensable. hot / cold test and defined maximum temperature differences that the material in the following test has survived unscathed. There is no carbon material that is completely blister For the test, identical specimens were heated to pre-defined temperatures and then submerged in ice water. The results resistant. were standardized; the temperature difference found for SSiC was selected as a reference value. Blistering can be generated with the help of special seal ring tests. Blister resistance indexes (IBL) have been defined to evaluate the damages caused by blister Classification of Thermal Shock Resistance formation: Material Relative Thermal Shock Resistance Blister resistance index I = 10 BL SSiC (sintered-silicon carbide) 1 ¬ Blister resistant material Figure 7: Typical appearance of blistering on a carbon SiSiC (reaction-bonded silicon carbide) 1 graphite sliding surface SiSiC-C (reaction-bonded graphite loaded silicon carbide) 1.15 Blister resistance index IBL = 0 ¬ not operable, because material has been destroyed SiC30 1.3 10 The results in Figure 8 show that the SiC30 material as a hard sliding partner has significantly improved the blistering 8 x resistance of carbon materials and that, when used as a The thermal shock resistance of SiC30 is superior 6 “soft carbon material” in a pairing, it can completely prevent to that of all current ceramics used in tribological tance inde is blistering. applications. st 4 re ter 2 Blis 0 resin impregnated resin impregnated SiC30/SiC30 carbon/steel carbon/SiC30 1.4136 Figure 8: Results of a series of blistering tests ¬ SiC30 avoids blistering ¬ SiC30 is the only blister resistant “carbon material” ¬ SiC30 as counterpart material significantly improves the blister resistance of carbon graphite Figure 9: SiC30 bearings 06 07 SIC30 – SILICON CARBIDE/GRAPHITE COMPOSITE MATERIAL SIC30 – SILICON CARBIDE/GRAPHITE COMPOSITE MATERIAL Chemical Resistance Designing with SiC30 Rotationally symmetric components or rectangular plates are suitable geometries. For different Many ceramic materials for tribological applications have limited chemical resistance to highly components the recommended dimensions are summarized in table 2. If possible, deviations corrosive media since their oxide or silicon-based bonding phase would corrode. from these guidelines should be avoided or at least discussed with our technical application service beforehand. SiC30 does not have any oxidic phases and also does not The material is resistant to: With regard to producability and cost the following recommendations should be observed: have any accessible free silicon. The excellent chemical ¬ aqueous salt solutions, ¬ no sharp changes in cross section resistance of the SiC30 material has been confirmed in ¬ organic reagents, ¬